The invention relates to a pivot assembly used as the bearing of a swing arm type actuator in a hard disk drive. More particularly, the invention relates to an improvement of the fixing means of a spacer which accomplishes spacing of ball bearings.
Conventional pivot assemblies include ball bearings fixed at both ends of a shaft. A spacing between outer rings of the ball bearings is accomplished by a ring shaped spacer.
A convex line is formed at an inner circumferential side edge of an end face of the spacer. The convex line protrudes in an axial direction of the spacer. Additionally, a concave part is formed at an inner circumference side edge of an end face of the outer ring. Convex lines of the spacer and the concave part of each outer ring are configured to be joined together such that the spacer is held between the outer rings. This pivot assembly is then bonded to a base of a swing arm having a magnetic head at its tip.
In the above-mentioned conventional pivot assembly, the spacer is held by joining a convex line of the spacer with a concave part of each outer ring. In such arrangement it is likely that the precision of the assembly becomes insufficient due to convex stripe machining errors. Particularly, the degree of parallelization of the spacer is typically insufficient. Additionally, the area of contact between an outer ring and the spacer is small, resulting in a reduced holding strength.
In the process of manufacturing the described conventional pivot bearing assembly, the convex line has to be machined to accomplished its precise shape and size. Therefore, the manufacturing process of such bearing assembly is complicated, resulting in higher manufacturing costs.
The above mentioned bonding of the swing arm and the pivot assembly must be performed in the conventional assembly because holding of the spacer is unstable. Therefore, if a defect occurs in one of the constituent parts the entire unit must be discarded, which is obviously uneconomical. Additionally, outgassing from the bonding agent brings about a harmful effect on the surface of the hard disk and magnetic head.
In conventional designs of the pivot assembly, it is common for the outer ring to have an abbreviated circular arc-shaped chamfer at the peripheral edge of its outer circumferential surface at its end face. When the outer diameter of the spacer is the same as that of the outer ring, a concave part is formed between them. In this case, the concave part the gap becomes smaller towards the inner part of the connection. If laser welding was to be used with this conventional assembly, a laser beam must correctly hit the line of contact between the spacer and outer ring positioned in the innermost part of the formed connection. Moreover, the laser beam must irradiate so as to follow the common tangent of the chamfer and the end face of the spacer. When these points are taken into consideration, in the event the laser beam is of a small diameter as mentioned above, where the position of the spacer fluctuates even slightly, the laser beam cannot irradiate the necessary place making laser welding, practically, impossible.